The invention relates to a picture display device having a vacuum envelope for displaying pictures composed of pixels on a luminescent screen, and particularly relates to a thin picture display device (i.e. a picture display device having a small "front to back dimension") which is clearly distinguished from state of the art display devices.
Typical state of the art approximations to thin-type picture display devices are devices having a transparent face plate whose inner side is provided with a phosphor pattern, one side of which is provided with an electrically conducting coating (the combination also being referred to as luminescent screen). If (video information-controlled) electrons impinge upon the luminescent screen, a visual image is formed which is visible via the front side of the face plate. The face plate may be flat or, if desired, curved (for example, spherical or cylindrical).
In a first category of thin-type picture display devices a number of thermally heated wire cathodes is arranged in a plane parallel to the luminescent screen at a location within the picture display device remote from the screen, which cathodes are responsible for producing the required electrons. The electrons produced may be present in the form of an electron cloud. In order to cause the electrons to impinge upon specific locations on the luminescent screen for forming a picture in such a device, the required electron current must be withdrawn from the cloud. This requires a stack form of addressing electrodes, (a buffer electrode), focusing electrodes, and in some cases deflection means. A problem which has hitherto occurred in such picture display devices is that they exhibit visual brightness variations.
Another category of picture display devices of the thin type uses single or multiple electron beams which initially extend substantially parallel to the plane of the display screen and are ultimately bent towards the display screen so as to address the desired areas of the luminescent screen either directly or by means of, for example a selection grid structure. (The expression electron beam is understood to mean that the paths of the electrons in the beam are substantially parallel, or extend only at a small angle to one another and that there is a main direction in which the electrons move.) The above-mentioned devices require, inter alia, complicated electron-optical constructions.
Moreover, picture display devices of the single beam type generally require a complicated (channel plate) electron multiplier of the matrix type, certainly if they have slightly larger screen formats.
A more extensive survey of the drawbacks of thin-type state of the art picture display devices has been given in EP-A 213,839, corresponding to U.S. Pat. No. 4,719,388.